Analysis of transverse cracking in cross-ply laminates: Weibull distribution based approach

Abstract: Composite laminates make up more than 50% of modern aircrafts. In such composite laminates, transverse/intralaminar cracking is usually the first form of damage appears and they tend to increase in number during the service life. The growth in number of these cracks significantly degrades the thermo-elastic properties of the composite laminate and eventually leads to final failure. Thus, it is important to predict this cracks growth in numbers and its effect in thermo-elastic properties degradation. In this study, transverse cracks in relatively thick glass fiber epoxy (GF/EP) cross-ply composite laminates under tension quasi-static and tension-tension fatigue loading [VRPG1] has been analyzed and predicted.In the first article attached here, increase in number of transverse cracks in [ ]s GF/EP laminates under tension quasi-static loading at room temperature (RT) are analyzed using 2 material systems. The failure stress distribution in 90 plies of the laminates is defined by Weibull distribution and the Weibull parameters are determined from crack density (=number of cracks per unit length) versus applied thermo-mechanical transverse stress in 90-layer ( ) data points within the non-interactive crack density region. The crack density growth is then predicted versus the   and applied mechanical strain in the laminate from the determined Weibull parameters using Monte Carlo method and the stress distribution models between adjacent cracks. The stress distribution models used here are the Hashin’s model and novel stress distribution model based on approach in which average transverse stress between the cracks in similar to FEM solution. As expected, the predicted crack density using Hashin’s model has underpredicted with respect to the test results, whereas the results using the novel stress distribution model were in good agreement with the non-interactive and interactive crack density regions of test results. The importance of using the Monte Carlo method and novel stress distribution model to predict the whole crack density region have been emphasized in the article, in addition to that it also redefined the interval of non-interactive crack density region. The second article is continuation of previous work but in tension-tension fatigue loading. It deals with the crack density analysis and prediction in [ ]s GF/EP laminate under fatigue loading at RT. The fatigue tests were performed at 3 constant stress levels. Here the Weibull parameters were determined from the data points within the non-interactive crack density region in quasi-static and fatigue loading. From the determined Weibull parameters of each stress level and using Monte Carlo method and the novel stress distribution model, the crack density versus the number of fatigue cycles were predicted and in good agreement with the fatigue test results at the respective stress level. The intention here is to use Weibull parameters of one constant stress to predict crack density at other stress levels. The results revealed that the dependence of the crack density with the stress level is underestimated, that results in different shape parameter. So, it is suggested to perform fatigue tests at two stress levels to predict reliable results.The suggestions in the second article have been described in the attached conference article by developing new methodology on crack density growth simulation and Weibull parameter determination in tension-tension fatigue loading. In the newly developed methodology, in detailed fatigue tests are performed at one stress level to obtain all data points and at higher stress level to obtain one data point that is crack density at certain number of cycles. Using the determined Weibull parameters from non-interactive crack density region, the whole crack density region was successfully predicted for arbitrary stress levels.